The value of optical networks incorporating all-optical cross connects (OCC) is typically associated with being able to selectively route individual channel wavelengths through several network nodes without performing optical-electrical and electrical-optical conversion.
From a network perspective, most research on the OCC architectures have been concentrated on the highest possible capability for the cross-connect itself. For example, switch architectures with single wavelength granularity and fully non-blocking capability are considered indispensable to optical networks and have, therefore, been a subject of intense research. The term “non-blocking” refers to an ability of the optical switch to direct any spectral input to any output without precluding (or “blocking”) any of the possible connections for other spectral inputs and outputs.
Typical OCC designs include:                (i). a spectral DEMUX on each input fiber, followed by a space-division switch, followed by a MUX or combiner to direct the selectively-switched wavelengths to output fibers;        (ii). a passive splitter after each input fiber, an optical filter on each split path, a space-division switch, followed by a combiner to direct filtered and selectively switched wavelengths to output fibers; and        (iii). a passive splitter after each input fiber, a filter on each split path, and a combiner to direct filtered wavelengths to output fibers.        
FIG. 1 illustrates a conventional “broadcast and select” OCC apparatus 100 of architecture of (iii) as described. In particular, FIG. 1 illustrates a fully non-blocking OCC. In this OCC architecture, N*(N−1) filters are required for cross-connecting N diverse routes.
The conventional OCC apparatus 100 includes a plurality of optical inputs 102 a plurality of optical outputs 104. The conventional OCC apparatus 100 apparatus also includes local cross-connect 110 used for cross connecting the optical inputs 102 and outputs 104 so that optical signals flowing into the optical inputs 102 are directed to the appropriate optical outputs 104.
The local cross-connect 110 itself includes a plurality of optical couplers 106 and a plurality of optical filters 120 optically placed between each connected pair of optical couplers 106. As seen, depending on the placement, each optical coupler 106 performs one of two functions—splitting the incoming optical signal for outputting to other optical coupler or combining optical signals from other optical couplers and outputting the outgoing optical signal.
In the example shown in FIG. 1, there are 4 diverse routes. Cross-connecting the 4 routes requires 12 optical filters. Increasing the route by one to total 5 requires eight additional filters to total 20. In short, the fabric of the conventional OCC architecture requires N*(N−1) filters. In other words, the increase is quadratic.
Generally, the conventional OCC architectures have optical signal flows that may be described as follows:
(1) split the incoming optical signal;
(2) perform optical filtering and/or switching; and
(3) recombine optical signals into output filters.
This is shown in FIG. 1 where there is an optical filter 120 after each split and before each recombine. Such design necessarily constrains the OCC to an effectively “localized” architecture since the optical processing is sandwiched between the splitter and combiner functions. Localization occurs when all of the optical switch components are required to be located at a single physical location in the network.
This localization, while perhaps enabling to maximize the capability of the OCC node itself, may not be required or needed for the network, which the OCC node is a part of, as a whole. Further, it may lead to unnecessarily complicated hardware and connections that make up the network, thereby increasing its cost.